A mechanism for managing concurrent access to shared data or resources by granting temporarily exclusive access to the processes requesting the lock.

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Rolling update to all rows in innodb table (no rollback if aborted)

I have the following table, which stores the Social Security Death Master File database (~86M rows): CREATE TABLE `death_master_files` ( `id` int(11) NOT NULL AUTO_INCREMENT, `ssn_an` smallint(5) ...
2
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1answer
79 views

Implications of setting READ_Write

I am looking to update several users on READ_ONLY databases. As the databases are used 24/7 globally, and maintenance windows have just past, I would like to do this during a low-activity moment (to ...
0
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1answer
85 views

I have a DB that is locking up from numerous updates to a table: Should I convert it from MyISAM to InnoDB?

FYI: I don't believe this is a duplicate question, I've looked and most are general questions with vague answers. See more specifics below: Currently a database I am in charge of locks up every once ...
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1answer
174 views

CONCURRENT SELECT's SLOW … LOCK IN SHARE MODE

My Table has 25 Million rows total and 6 million rows satisfying below where clause. Select 1: select max(stamp) from Table where type = "string" LOCK IN SHARE MODE ; 6000+ seconds Select 2: ...
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0answers
241 views

Postgresql: Update or insert stuck

I'm running update-or-insert query on a table of approximatelly 3mln rows, 4 columns. Query is part of every day process, and for same days, the query stucks forever. It's just blocked. It's ...
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2answers
129 views

mysql write lock

I dont add any manual locking or any transaction anything, just manual running queries from php script, and execute below two update queries at the same time update table_x set status = 'PROCESSING' ...
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1answer
58 views

Deadlock scenario, where is this S lock coming from?

I am encountering the below deadlock scenario. Please see the attached object definitions and execution plans. The plans were pulled out of cache from a system where this deadlock does occur. I ...
3
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1answer
368 views

How to perform server-side transaction timeout if COMMIT TRANSACTION will never arrive?

How can SQL Server terminate one of its transactions if it exceeds preset timeout? Imagine the following transaction performed by traveling salesman's SQL client application, which is submitted ...
3
votes
1answer
115 views

Will dropping text column on SQL Server 2014 lock the table?

I have been tasked to drop a text column from a production SQL Server 2014 table. The table contains 61,683,821 records. Question: will dropping the column lock the table (or cause similar ...
1
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1answer
656 views

MySQL: SELECT GET_LOCK slow/timeout

I am using "Zebra Session" as a replacement for PHP's built-in session management. Zebra Session stores sessions in a MySQL database, and uses "session locking" in order to ensure that data is ...
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0answers
224 views

Getting Waiting for table metadata lock for select statements

I am using MySQL server 5.6.23 on CentOS and server configuration is like RAM - 32 GB Cores - 6 cores Innodb buffer pool size = 8 GB Key cache size = 2 GB We are using only select queries. But all ...
5
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1answer
354 views

SELECT RELEASE_LOCK causing “Mysql has gone away”

During a long running process (90m+), our code calls SELECT RELEASE_LOCK('..');. However it always gives a "Mysql has gone away" error when we do this. We never got to see the return value of the ...
3
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1answer
218 views

Work queue with complex select and long processing: Ensuring concurrency

I have a queue table from which worker processes claim records, one at a time. It is crucial that no two workers claim same item to process. Normally this kind of thing is done with select top (1) ...
2
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0answers
62 views

SQL Server 2008 R2 - Should I be worried at this statistics regarding indices causing locks?

We have some mild table locking issue during our peak hours so I figured the following query query taken from this site would be a good start. And boy, does it show me some seriously concerning ...
2
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2answers
872 views

Is it safe to cancel a PostgreSQL ALTER TABLE query that is waiting on a lock?

We started an ALTER TABLE query hours ago and only recently realized (via pg_stat_activity) that it is waiting on a lock. We discovered the other query that is holding a lock on the table we want to ...
3
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0answers
366 views

Slow transactions, many locks

At high load conditions the server app stops responding to client because begin/commit statements are executing very slowly (some take 15 seconds). The queries are simple - insert, update two columns ...
1
vote
1answer
349 views

What happens if two mySQL queries both try to lock the same row at the same time?

So this isn't exactly my strong suit, but here's my basic understanding of the situation: If two threads of the same application both try to execute the same query at the same time, mySQL will ...
0
votes
1answer
1k views

How to update a (very) large table without locking in MySQL

I have a large table (58+ million records) which represents a relation between two records (player and target) in a second table. Unfortunately, whoever designed our schema didn't think things ...
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1answer
184 views

When does SQL Server acquire locks?

The list of isolation levels in SQL Server found here states that write locks acquired within a transaction are retained until the end of the transaction. However it doesn't mention anything about ...
3
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1answer
306 views

(How) does table inheritance interfere with locking in postgres?

I have a table inheritance setup that might be simplified like this: CREATE TABLE p ( id BIGSERIAL PRIMARY KEY, type_id BIGINT, approved BOOLEAN ); CREATE INDEX ON p(approved); CREATE ...
1
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0answers
69 views

Average Waiter Count increasing

I am in a nightmare. We have deployed an application to a UAT environment, which has only 7 users. Since then, we have noticed in the logs, a lot of deadlocks, and processes being victims and things. ...
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2answers
251 views

SQL Server - Slow Database for no apparent reason [closed]

I have a DB Server running SQL Server 2008 R2 SP2 on 24 physical Cores and 32GB of RAM. The database files are on a SSD Raid1 and the TempDB on a SAS 15k (150GB DB) I assume that the server has more ...
3
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1answer
121 views

enabling snapshot isolation level on a database - what to monitor?

I am having problems with frequent deadlocks on a subscription database. I am considering enabling the snapshot isolation level for that database. I am aware that there is an overhead on the tempDb ...
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1answer
151 views

GET_LOCK([name], 0) behaviour and multiple GET_LOCK() order

I read from the documentation that the behavior of distributing a lock requested by many connections after RELEASE_LOCK is called from the connection holding the lock is undefined. I was curious: say ...
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1answer
149 views

Check for table lock in conditional statement [closed]

How can I make this work? IF( EXISTS (SHOW OPEN TABLES WHERE In_use < 2 and `Database` like 'MYDB' ) ) THEN -- DO SOMETHING END IF Context I want to run some sql statements inside a procedure, ...
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2answers
773 views

SQL Server Index Update Deadlock

I have 2 queries which when run at the same time are causing a deadlock. Query 1 - update a column which is included in an index (index1): update table1 set column1 = value1 where id = @Id Takes ...
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2answers
299 views

Determine whether there is any blocking while deleting large number of records [closed]

I would like to know whether there is any way to determine why it is taking too much time say 3 minutes for deleting 50K records from a database hosted in Sql Azure. I have clustered index on primary ...
0
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1answer
409 views

Concurrent SELECT and UPDATE in multiprocessing python

I have to randomly match about 20 million rows in two tables without using the same row twice using PostgreSQL 9.3.5. Both tables have the following structure CREATE TABLE de_sim_points_end ( -- ...
5
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2answers
105 views

New Index on table cause table to be locked really often

Here are my tables : CREATE TABLE [dbo].[Trackers] ( [IdTracker] INT IDENTITY (1, 1) NOT NULL, [IMEI] NVARCHAR (16) NULL, [CreationDate] ...
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3answers
4k views

When is it safe to disable InnoDB doublewrite buffering?

MySQL InnoDB allows us to disable doublewrite buffering by setting innodb_doublewrite = 0. Other databases doesn't seem to allow this setting to be tweaked. How could InnoDB still be able to maintain ...
1
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1answer
2k views

Many transactions are getting stuck in the “cleaning up” state - what could cause that?

I'm trying to track down a locking issue, and found via SHOW PROCESSLIST that when the queries in question are waiting for locks and timing out, there are no other queries active in the process list. ...
6
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1answer
2k views

SELECT INTO OUTFILE vs INSERT INTO … SELECT

During my cursory research I have not been able to find a definitive answer on the benefits that SELECT INTO OUTFILE provides over INSERT INTO ... SELECT. Upon reading the docs related to INSERT INTO ...
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2answers
620 views

Alter table statement waiting (for hours, on dev machine), but no locks shown

I have been trying to issue a simple: ALTER TABLE tablename ADD COLUMN id_col character varying (30) type statement on a Postgres 9.1.13 build on Debian. The application is still in private beta, so ...
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2answers
1k views

Writing a large update/delete script that doesn't provoke locks

While running a T-SQL script that is performing massive amounts of deletes, I had the unpleasant experience of causing some sort of lock contention that prevented inserts of data in some tables for ...
0
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1answer
456 views

Sybase ASE lock table to disallow users insert values

I need to disallow users to insert values in some table, for example for a 5 mins. Seems I should use at isolation clause but can't figure out how to use it. Thanks
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1answer
200 views

InnoDB & Isolation Levels - Aren't repeatable reads a bad thing?

I was reading about InnoDB's isolation levels and it makes sense for the most part, but what I don't get is why are unrepeatable reads a bad thing? Shouldn't it be the other way around? For examples: ...
6
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2answers
527 views

Is this update, select combination query thread safe?

I have a table called seats, which has a schema like this id,taken For each user, I take a random untaken id and assign to that user, here for simplicity say, I make taken =1. The query I am ...
2
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1answer
556 views

How many rows will be locked by SELECT … ORDER BY xxx LIMIT 1 FOR UPDATE?

As was asked on stackoverflow but then for MySQL, I was wondering how this works in PostgreSQL. How many rows get locked when I do a "FOR UPDATE" in combination with a "LIMIT", a "ORDER BY" and some ...
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0answers
77 views

Handling this multi-threading scenario in the database?

I am working on sample bus ticket booking application,in I am facing these two multi-threading scenarios. Scenario 1 1: Let's say there are two users, they both pick a particular seat and submit ...
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0answers
32 views

MySQL - Transactions and causality

I'm new to MySQL's LOCK and TRANSACTION and have a question about different isolation levels of a transaction: Given two transactions executing the same code (auto-commit is false): (1) get data of ...
2
votes
1answer
441 views

Do MongoDB's “read uncommit” and “write lock” conflict with each other?

I was reading the MongoDB documentation, where it says about read uncommit: MongoDB allows clients to read documents inserted or modified before it commits these modifications to disk, regardless of ...
2
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1answer
363 views

How mysql (innodb) handles auto increment column

I am working on a OLTP environment with multiple parallel write operation. I found this in documentation about auto increment locking but still i am interested to know much about it in details. Can ...
0
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1answer
983 views

What does it mean when I see a lock in sys.dm_tran_locks and there's no matching row in sys.dm_exec_requests?

I'm running this query select sessions.session_id from sys.dm_tran_locks locks inner join sys.dm_exec_sessions sessions on locks.request_session_id=sessions.session_id and it consistently ...
4
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2answers
387 views

Strategies for “checking out” records for processing

I'm not sure if there is a named pattern for this, or if there isn't because it's a terrible idea. But I need my service to operate in an active/active load balanced environment. This is the ...
0
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0answers
91 views

How can I obtain concurrent deletes for this table?

We have a program that is currently doing something to the effect of: SET TRANSACTION ISOLATION LEVEL READ COMMITTED BEGIN TRANSACTION UPDATE [Source].[dbo].[SourceTable] SET [ProcessedOn] = ...
1
vote
1answer
283 views

Why would I not specify ROWLOCK to get rid of page locks?

I have a query that goes something like this: SELECT TOP (1) * FROM MyTable WITH (UPDLOCK, READPAST) ORDER BY SomeColumn ASC; This answer says that it's hard to say for sure but it will probably ...
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2answers
305 views

One of databases in MongoDB suddenly gets high lock %

I observe repeatable, sudden, short-time update queries slowdowns in MongoDB cluster for single database. That slowdowns lasts about 30 seconds and repeats few times a day. I found that lock % and ...
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0answers
244 views

Postgres advisory lock deadlocks itself?

I am executing pg_advisory_locks using the following set of statements: SELECT pg_advisory_lock(317,2); UPDATE posts SET dislikers = array_remove(dislikers, 7) WHERE id = 317; update posts set ...
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1answer
514 views

MySQL 5.6 replication causes 'waiting for table lock'

All of the sudden queries on slave server stopped with status "Waiting for table level lock" I restart mysql service and stop replications and locking does not show up anymore. Once I turn ...
12
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1answer
38k views

Detecting the locked table or row in SQL Server

I'm trying to understand/learn how to track down the details of a blocked session. So I created the following setup: create table foo (id integer not null primary key, some_data varchar(20)); ...